Boost Gauge T-fitting Size?

[NewSouth]

I did a search and couldn't find any specifics on this....

If I want to attach a mechanical boost gauge, what size t-fitting do you need to fit on the supercharger tubing?

Or what size (ID) tubing is it? That way I can test the t-fitting so it's the right size and I won't have to use zip ties to seal it.

Thanks!!